1. Field of the Invention
This invention relates to an integrated circuit package and in particular to a support assembly for integrated circuit chips.
2. Description of the Prior Art
Integrated circuits (IC) generally comprise a number of gates or flip-flops that are packaged in a single IC container. The IC package provides input and output pins, pads, or leads which are connected to plated strips on circuit boards or other means to form a complete circuit of which the IC is a part. The IC chips are packaged by die attachment to paddles of lead frames. The lead frames are either stamped or etched according to the quantity to be made. In the event that a large quantity is to be produced, then stamping techniques are employed. On the other hand, if only a small quantity of frames are needed, then they may be made by slower photolithography and etching techniques. The etching techniques allow finer tolerances than the stamping method. After die attachment, the bond pads of the device are connected to the leads of the lead frame by means of a fine metallic wire. Upon completion of the chip to frame interconnection, the chip and interconnections are encompassed by the IC package.
One problem that is encountered with stamped frames is the limitation of the space between the leads and components of the IC assembly imposed by the thickness of the metallic frame. The acceptable space between leads is approximately 1.5 times the thickness of the metal, which generally is a copper sheet of about 0.008 inches thick, for example.
Therefore, the spacing between leads that is required is at least 0.012 inches. If 25 leads, by way of example, are to be provided, then a total spacing of 0.300 inches is needed. This spacing creates too large a distance between the IC device, which is located centrally on the frame, and the leads at the periphery of the frame. Therefore a lower yield in production is obtained due to excessive length of the interconnecting wires. Also, the extra length required does not allow for a compact assembly with dimensions that are required by IC technology. The problem is compounded when the number of leads is increased thus necessitating a significant increase in space of the IC and the frame leads.
On the other hand, if a relatively thin tape-like support is used, such as an 0.001 inch thick metallic sheet, the spacing requirement is substantially reduced so that the leads can be located close to the IC device. However, such thin metal tapes of this type are too flexible and are not rigid enough for assembly.